Systemic Sclerosis (SSc) is a disease of unknown origin characterized by excessive deposition of collagen and other connective tissue macromolecules in skin and multiple internal organs. The most apparent and almost universal clinical features of SSc are related to the progressive fibrosis of the skin, the microvasculature, and numerous internal organs. Well validated biomarkers that allow early diagnosis and assessment of disease activity or that carry a predictive prognostic value are not available for SSc. The development of objective and reliable markers reflecting the extent and severity of tissue fibrosis would be of invaluable assistance in determining the efficacy of a given treatment in clinical trials by offering an objective method that provides unbiased information which allows a reduction in the number of patients required to obtain statistical significance. Availability of such markers will also be of substantial value in the evaluation of therapeutic responses to disease modifying agents in the clinical management of SSc patients. Objective/Hypothesis: Our preliminary data strongly support the premise that proteomic analysis of the SSc fibroblast secretome can identify proteins that reflect fibroblast activation and the extent and severity of their profibrotic biosynthetic phenotype, and that these proteins are detectable in skin biopsies and sera of SSc patients. Based on this premise, we propose to test in this application the hypothesis that: "the identification by proteomic studies of the most differentially expressed proteins in the SSc fibroblast secretome compared to the secretome of normal fibroblasts followed by the validation of the results in serum from SSc patients will lead to the identification of highly reliable and specific biomarkers that can be used for early diagnosis and for assessment of extent and severity of tissue fibrosis in SSc". We propose to test the hypothesis with the following Specific Aims: SPECIFIC AIM 1: To identify by proteomic analysis the most highly differentially expressed proteins in the SSc fibroblast secretome compared to the secretome of normal dermal fibroblasts. SPECIFIC AIM 2: To validate the specificity of the proteins identified by proteomic analysis as a biomarker for SSc in sera from SSc patients by ELISA or Multiple Reaction Monitoring (MRM). SPECIFIC AIM 3: To determine the clinical value of the identified proteins by establishing correlations with relevant clinical parameters. The successful outcome of this project will lead to the identification of novel outcome measures for SSc that will have a transforming impact in the design and analysis of clinical trials for SSc and in the clinical management of patients affected by this incurable, disabling, and often fatal disease. PUBLIC HEALTH RELEVANCE: The identification of novel biomarkers for Systemic Sclerosis employing proteomics will lead to the identification of novel outcome measures for Systemic Sclerosis that will have a transforming impact in the design and analysis of clinical trials for Systemic Sclerosis and in the clinical management of patients affected by this incurable, disabling, and often fatal disease.